In order to meet a requirement for miniaturizing and thinning an electronic device, a method has been adopted that finely miniaturizes a semiconductor chip pattern, and that mounts semiconductor chips on both sides of a wired board, thereby increasing a mounting efficiency.
An example of a semiconductor-mounted device mounted with semiconductor chips on both sides of a wired board is shown in FIG. 10. Electrode pads (not shown) of a wired board 2 and projecting electrodes 4 of a semiconductor chip 3 are electrically and mechanically connected at opposite positions of both sides of the semiconductor-mounted device 8, the wired board 2 and the semiconductor chip 3 being adhered by underfill resin 5.
A method for producing the semiconductor-mounted device is shown in FIGS. 11(a)-(c). As shown in FIG. 11(a), first of all the wired board 2 is put on a stage 6 with a heating apparatus (not shown), the electrode pads (not shown) on the wired board 2 and the corresponding projecting electrodes 4 of the semiconductor chip 3 being put together and connected by applying heat and pressure. As shown in FIG. 11(b), the underfill resin 5 is then introduced between the wired board 2 and the semiconductor chip 3, the wired board 2 and the semiconductor chip 3 being adhered by heat-hardening. Alternatively, the underfill resin 5 may be applied on the wired board 2 or the semiconductor chip 3 before the connection of the projecting electrodes 4 explained in FIG. 11(a) and then be simultaneously heat-hardened when the projecting electrodes 4 are connected. As shown in FIG. 11(c), the wired board 2 is then turned over, put on the stage 6 and provided with another semiconductor chip opposite to the semiconductor chip mounted on the other side of the wired board 2 in the same way as above.
In the above-mentioned semiconductor-mounted device and the producing method thereof, however, the positions at which the semiconductor chips are mounted on the both sides of the wired board have to be opposing each other across the wired board because it is necessary that pressure is applied to connect the electrode pad of the wired board and the projecting electrode of the semiconductor chip. When the positions are not opposing each other across the wired board, the wired board 2 warps on applying pressure on the semiconductor chip 3 as shown in FIG. 12, so the projecting electrode 4 can not contact with the electrode pad (not shown) of the wired board 2, thereby causing an open defect.
Therefore, it has been necessary to mount the semiconductor chips with almost the same size on the positions opposing each other across the wired board. This has largely restricted the constitution of the semiconductor-mounted device.
On the other hand, in Japanese Patent Gazette of Patent No. 2634351 (Pages 2-4, FIG. 1), a method is disclosed in which surface mount ICs that are not necessary to apply pressure for its mounting are mounted on positions not-opposing each other across a wired board, as shown in FIG. 13.